1,1'-dimethyl-4,4' bipyridylium or methyl viologen, a one equivalent redox dye, has been in use as a highly effective herbicide for the past twenty years. This product, known as paraquat, manifests an unusual toxicity in humans and animals when its route of administration is either oral or parenteral. More than 125 human deaths have resulted from accidental or intentional paraquat ingestion since its appearance as a commercial agricultural product. From all studies on the action of this toxic agent, there is no doubt that the target organ is the lung and that the cause of death is due to a progressive and inexorable loss of pulmonary function. There is no agreement, however, amongst interested research groups upon the basic toxic mechanism of action of paraquat. Because of this, a rational and effective therapy for toxic incidents has not been developed. In view of the interest and the need, it is proposed that a symposium entitled, "Biochemical Mechanisms of Paraquat Toxicity", be held in Iowa City, Iowa on June 28-29, 1976. A proposed program has been developed consisting of presentations of research in basic mechanisms rather than of clinical data. The benefits of such an information exchange at this time appear to be considerable for the encouragement of useful research advances in the field.